IN reply to Prof. Tait's criticism (NATURE, December 31, 1891, p. 199) of my paper (December 17, p. 152), I wish to say that I certainly do not consider Van der Waals's b as an absolute constant ...

The van der Waals equation of state is based on a simple, but realistic, physical model and therefore always yields physically meaningful results. Its quantitative deficiencies are due to the ...